Manny Gomez created a shopping list on Amazon.com just to keep track of some auto parts he wanted to buy. But as the holidays approached, he thought it wouldn't hurt to share the list with family and friends.

It just clicked, said Gomez, who added a selection of shoes, shirts and video games before posting his list online last week. I said, 'You know what? This would also make a great wish list.'

Gomez, 29, is one of a growing number of Americans going online to share exactly what they want for the holidays, a new twist on traditional registries for weddings or baby showers.

While it is culturally acceptable to register desired gifts for major life events to let newlyweds or new parents avoid the hassle of returns, some question its application to the holiday season, when giving is supposed to be better than receiving.

If you think a Christmas gift is supposed to express thoughtfulness or care or consideration, then the Christmas registry idea is missing the boat, said Barbara Kahn, a marketing professor at University of Pennsylvania's Wharton School.

Economists have said gift-giving is not efficient because people do not always get what they want, Kahn said.

On the other hand, she said, If someone knows me well enough to get me exactly what I want, without my having to tell them, well, that's the sweet spot.

Losing that sweet spot hasn't stopped retailers. More than six in 10 included holiday wish lists on their websites last year, up from 57 percent in 2008 and 55 percent in 2007, according to the National Retail Federation.

Such lists began as a way for relatives to choose presents for young grandchildren or nieces and nephews. But the idea is gaining momentum among teenagers and young adults who have less compunction about keeping their desires a secret.

Foot Locker Inc put up an online wish list a year ago, and apparel and shoe retailer Kenneth Cole Productions added one this year, displaying it prominently on its website with the message: Be careful what you wish for.

TURNING WISHES INTO CASH

From October through December, wish lists bring in about 15 percent of online sales for retailers that offer the feature on their websites, said Fiona Dias, an executive vice president of GSI Commerce Inc.

That compares with about 1 percent year round, said Dias, whose company operates more than 100 online stores for chains including Toys R Us, Aeropostale Inc and Bath & Body Works.

Dias said wish lists could be a wise long-term investment for retailers, especially if the informal, youth-oriented phenomenon evolves into a more traditional and lucrative registry business.

Toys R Us declined to specify how many sales come through its kid-friendly wish list, but Greg Ahearn, vice president for marketing and e-commerce, said it was increasingly popular.

When those presents are opened, and that kind of 'wow' factor comes, it will be a 'wow' because children have gotten what they hoped for, he said.

Ahearn said the wish list was just an extension of a long tradition of children writing letters to Santa Claus to communicate the gifts they're hoping to get.

The combined number of holiday and birthday lists at Toys R Us is only slightly below that of the Babies R Us registries, Ahearn said.

Other retailers said wedding and baby registries are still far more popular, but that could change as the Internet generation gets older.

It was just gauche, as an adult, to put your list of products out there, Dias said. But as I talk to people in their 20s, and maybe because they just grew up with online wish lists, they think it's actually pretty natural.

J.C. Penney Co Inc, Target Corp and other retailers have applications that allows shoppers to access registries via iPhones and other smartphones, an innovation that could get more people to use wish lists.

Starting in 2011, you're going to see a lot of process automation that makes that registry a really, really powerful utility that's integrated with social networks and the like, said David Sikora, chief executive officer of mobile retail company Digby.

All that technology will just make it easier for wish-list fans to cast their net more widely. Gomez, a computer engineer from Belleville, New Jersey, had no reservations about sharing his list on the social network site Facebook.

It posts it on my wall, Gomez said, and everybody I let see my wall can see my list.

(Reporting by Jon Lentz; Editing by Michele Gershberg and Lisa Von Ahn)